In magnetic recording, one of the indicators of performance is that a magnetic recording medium with large magnetic coercive force can be used. There is an idea from a long ago, in which a high-frequency field is applied to the magnetic recording medium during magnetic recording to temporarily weaken the magnetic coercive force of a recording area, and then a recording bit is formed by a head magnetic field. For example, JP 7-244801A (1995) (Patent Literature 1) discloses a recording method of applying Joule heating or magnetic resonance heating to a magnetic recording medium by a high-frequency field to locally reduce the magnetic coercive force of medium.
Along with the improvement in the areal recording density, a recording system called “microwave assisted magnetic recording” that also uses the high-frequency is focusing attention again in recent years. In the microwave assisted magnetic recording, a high-frequency field of a strong microwave band is applied to an area of nanometer order to locally excite a recording medium to reduce a switching field to record information. Since the magnetic resonance is used, a large reduction effect of the switching field cannot be obtained unless a high-frequency field with a strong frequency proportional to a magnetic anisotropy effective field of the recording medium is used.
JP 2005-025831A (Patent Literature 2) discloses a high-frequency oscillation element intended for microwave assisted magnetic recording, the element having a structure including a laminate file with a structure similar to a GMR element (giant magnetoresistance effect element) placed between electrodes. The element can inject conduction electrons with spin fluctuation generated in a GMR structure to a magnetic material through a non-magnetic material to generate a minute high-frequency oscillation magnetic field. Similarly, Nature 425, 380 (2003) (Non Patent Literature 1) reports microwave oscillation based on a spin torque.
“Microwave Assisted Magnetic Recording” described in TMRC 2007-B6 lecture proceeding (Non Patent Literature 2) discloses a technique, in which a magnetization fast rotating body (Field Generation Layer: hereinafter, abbreviated as “FGL”) that is rapidly rotated by the spin torque is arranged near a magnetic recording medium adjacent to a main pole of a perpendicular magnetic head to generate a microwave (high-frequency field), and information is recorded in the magnetic recording medium with large magnetic anisotropy.